Electro-optical switching using coupled photonic crystal waveguides

ABSTRACT

An electro-optical switch implemented in coupled photonic crystal waveguides is disclosed. The switch is proposed and analyzed using both a finite-difference time-domain (“FDTD”) method and a plane wave expansion (“PWM) method. The switch may be implemented in a square lattice of silicon posts in air, as well as in a hexagonal lattice of air holes in a silicon slab. Switching occurs due to a change in the conductance in the coupling region between the photonic crystal waveguides, which modulates the coupling coefficient and eventually causes switching. Conductance may be induced electrically by carrier injection or optically by electron-hole pair generation. The electro-optical switch has low insertion loss and optical crosstalk in both the cross and bar switching states.

CROSS-REFERENCE TO RELATED APPLICATIONS AND CLAIM FOR PRIORITY

The present application is a U.S. National Stage application filed under35 U.S.C. § 371, claiming priority of International application No.PCT/US03/01384, filed Jan. 17, 2003, and U.S. Provisional PatentApplication Ser. No. 60/350,749, filed Jan. 22, 2002, under 35 U.S.C. §§119 and 365, the disclosures of the above-referenced applications beingincorporated by reference herein in their entireties.

BACKGROUND OF THE INVENTION

A. Field of the Invention

The present invention relates generally to photonic crystals, and, moreparticularly to electro-optical switching using coupled photonic crystalwaveguides.

B. Description of the Related Art

During the last decade photonic crystals (also known as photonic bandgapor PBG materials) have risen from an obscure technology to a prominentfield of research. In large part this is due to their unique ability tocontrol, or redirect, the propagation of light. E. Yablonovich,“Inhibited spontaneous emission in solid-state physics and electronics,”Physical Review Letters, vol. 58, pp. 2059-2062 (May 1987), and S. John,“Strong localization of photons in certain disordered dielectricsuperlattices,” Physical Review Letters, vol. 58, pp. 2486-2489 (June1987) initially proposed the idea that a periodic dielectric structurecan possess the property of a bandgap for certain frequencies in theelectromagnetic spectra, in much the same way as an electronic bandgapexists in semiconductor materials. This property affords photoniccrystals with a unique ability to guide and filter light as itpropagates within it. Thus, photonic crystals have been used to improvethe overall performance of many optoelectronic devices.

The concept of a photonic bandgap material is as follows. In directconceptual analogy to an electronic bandgap in a semiconductor material,which excludes electrical carriers having stationary energy stateswithin the bandgap, a photonic bandgap in a dielectric medium excludesstationary photonic energy states (i.e., electromagnetic radiationhaving some discrete wavelength or range of wavelengths) within thatbandgap. In semiconductors, the electronic bandgap results as aconsequence of having a periodic atomic structure upon which the quantummechanical behavior of the electrons in the material must attaineigenstates. By analogy, the photonic bandgap results if one has aperiodic structure of a dielectric material where the periodicity is ofa distance suitable to interact periodically with electromagnetic wavesof some characteristic wavelength that may appear in or be impressedupon the material, so as to attain quantum mechanical eigenstates.

A use of these materials that can be envisioned, is the optical analogto semiconductor behavior, in which a photonic bandgap material, or aplurality of such materials acting in concert, can be made to interactwith and control light wave propagation in a manner analogous to the waythat semiconductor materials can be made to interact with and controlthe flow of electrically charged particles, i.e., electricity, in bothanalog and digital applications.

Planar photonic crystal circuits such as splitters, highQ-microcavities, and multi-channel drop/add filters have beeninvestigated both theoretically and experimentally in both two- andthree-dimensional structures. For two-dimensional photonic crystalstructures, the photonic crystal will be either perforated in aninfinitely thick dielectric slab or formed of infinitely long dielectricrods. In-plane light confinement is achieved in such structures bymultiple Bragg reflections due the presence of the photonic crystal. Forthree-dimensional photonic crystal structures, confinement in verticaldirection is achieved by total internal reflection (TIR).

Work on photonic crystal waveguided components is now moving towards thedevelopment of photonic bandgap integrated circuits (PBGICs) in which avariety of active and passive optical components are integratedmonolithically on a chip. Electro-optical switches are key components ofsuch PBGICs, yet only one proposal for implementing such switches—aresonator device—has appeared in the literature. See S. Fan et al.,“High Efficiency Channel drop filter with Absorption-Induced On/OffSwitching and Modulation,” USA (2000).

Thus, there is a need in the art for an electro-optical switching devicefor PBGICs that addresses the needs of the related art.

SUMMARY OF THE INVENTION

The present invention solves the problems of the related art byproviding electro-optical switching using coupled photonic crystalwaveguides. The switching mechanism is a change in conductance (σ) inthe coupling region between two evanescently coupled photonic crystalwaveguides. Conductance is induced electrically by carrier injection oris induced optically by electron-hole pair generation. The presentinvention provides real time optical signal processing by utilizingoptical switching in photonic crystals over a small area which willfacilitate future integration with optical integrated circuits.

The present invention provides a new technique for switching anelectromagnetic wave propagating through photonic crystal waveguides.Electromagnetic waves can be either in the microwave or optical regime,based upon the constituent materials of a photonic crystal. Theinvention makes use of coupled photonic crystal waveguides, where thecoupling coefficient between nearby waveguides can be modulated via anexternal electrical or optical means.

Further scope of applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description. Itis to be understood that both the foregoing general description and thefollowing detailed description are exemplary and explanatory only andare not restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus are not limitativeof the present invention, and wherein:

FIG. 1 is a schematic top plan view of a coupled photonic crystalwaveguided (CPhCW) system consisting of two closely coupled PBGwaveguides separated by two PBG layers of coupling length L_(c), inaccordance with an aspect of the present invention and wherein thesystem is formed using a periodic array of silicon pillars arranged insquare lattice;

FIG. 2( a) is a dispersion diagram for the CPhCW system shown in FIG. 1obtained using a plane wave expansion (“PWM”) method and afinite-difference time-domain (“FDTD”) method, where the dashed linecorresponds to FDTD results and the solid line corresponds to PWMresults;

FIG. 2( b) is a graph showing modal dispersion curves of the eigenmodesof the CPhCW system shown in FIG. 1, where the odd mode is the highfrequency mode and the even mode is the low frequency mode, and astraight line drawn from a normalized frequency axis will intersect withthe two curves from which modal propagation constants of the even andthe odd modes can be determined and hence the coupling length L_(c) canbe calculated;

FIG. 2( c) is a dispersion diagram for the CPhCW system shown in FIG. 3;

FIG. 2( d) is a graph showing modal dispersion curves of the eigenmodesof the CPhCW system shown in FIG. 3, where the odd mode is the lowfrequency mode and the even mode is the high frequency mode, and astraight line drawn from a normalized frequency axis will intersect withthe two curves from which modal propagation constants of the odd andeven modes can be extracted and used to calculate the frequencydependant coupling length L_(c);

FIG. 3 is a schematic top plan view of a CPhCW system consisting of twoclosely coupled PBG waveguides separated by two PBG layers of couplinglength L_(c), in accordance with another aspect of the present inventionand where the system is formed using a periodic array of air holesarranged in a hexagonal lattice;

FIG. 4 is a graph showing the calculated switching characteristics ofthe CPhCW system shown in FIG. 1; and

FIG. 5 is a graph showing the calculated switching characteristics ofthe CPhCW system shown in FIG. 3.

DESCRIPTION OF EMBODIMENTS OF THE PRESENT INVENTION

The following detailed description of the invention refers to theaccompanying drawings. The same reference numbers in different drawingsidentify the same or similar elements. Also, the following detaileddescription does not limit the invention. Instead, the scope of theinvention is defined by the appended claims and equivalents thereof.

The present invention presents the conception, modeling and simulationof a PBG channel-waveguided directional coupler switch that utilizeselectrically or optically induced loss (conductivity) in the couplingregion between two coupled waveguides.

1. Design Procedure

When two photonic crystal (“PhC”) waveguides are brought in closeproximity to each other they form what is known as a directionalcoupler. FIG. 1 shows a coupled photonic crystal waveguided (CPhCW)system in accordance with one aspect of the present invention andgenerally designated as reference numeral 10. CPhCW system 10 includestwo closely coupled PBG waveguides 12, 14 separated by two PBG layers ofcoupling length L_(c). Waveguide 12 includes two input/output ports,Port 1 (20) and Port 2 (22), and waveguide 14 has two input/outputports, Port 3 (24) and Port 4 (26). CPhCW system 10 may be formed usinga periodic array of silicon pillars 16 arranged in a square lattice 18.Under suitable conditions, an electromagnetic light wave 100 launchedinto one of the waveguides 12 or 14 can couple completely into theadjacent waveguide 12 or 14. Once the light wave 100 has crossed over,the light wave 100 couples back into the launching waveguide 12 or 14 sothat the power is exchanged continuously and as often as coupling lengthL_(c) between the two waveguides 12, 14 permits. However, a completeexchange of optical power at all wavelengths is only possible betweenmodes that have equal phase velocities or equal propagation constants.More specifically, the propagation constants must be equal for eachwaveguide in isolation. Equality of propagation constants, also known asphase synchronization, occurs naturally when the two waveguides areidentical. In that case, all the guided modes of both waveguides are inphase synchronism and can couple to each other at all wavelengths,providing complete exchange of optical power.

The CPhCW system 10 shown in FIG. 1 is no longer a single mode device,which would be the case if both waveguides were fused together into onewider waveguide that is not a single mode waveguide. Instead, CPhCWsystem 10 has two eigenmode solutions, an even (symmetric) mode and anodd (anti-symmetric) mode, which have slightly different propagationconstants and hence they propagate at different velocities. In order tocalculate the coupling length L_(c) necessary for a certain wavelengthto completely cross over from first waveguide 12 to second waveguide 14,or vice versa, the frequency dependant propagation constant of the evenand odd modes must be defined first, also known as the modal dispersionrelation of the CPhCW system 10 of coupled waveguides 12, 14. In orderto determine this relation, a computational unit cell (a “Supercell”)shown in the bottom right corner of FIG. 2( a) is used since thestructure is periodic.

For numerical experiments a directional coupler is first built using twosingle mode 2D-PhC waveguides, obtained by removing a row from a squarelattice of infinitely long dielectric rods (or silicon pillars) in anair background. By way of example only and not limitation of the presentinvention, the design parameters for the photonic crystal may be definedas follows. The dielectric rods may have a dielectric constantε_(r)=11.56 and a radius r=0.2a, where a is the lattice constant of thecrystal. Using these values the structure was found to have a completebandgap in the spectral range of 0.23≦a/λ≦0.41 for TM polarization(magnetic field in plane).

The structure shown in FIG. 1 may be numerically analyzed using eitherthe plane wave expansion (PWM) method disclosed in M. Plihal et al.,“Photonic band structure of two-dimensional systems: The triangularlattice,” Phys. Rev. B, vol. 44, pp. 8565-8571 (1991), or thefinite-difference time-domain (FDTD) method disclosed in D. Hermann etal., “Photonic Band Structure Computations,” Opt. Express, vol. 8, pp.167-172 (2001), and A. Taflove et al., Computational Electrodynamics:The Finite-Difference Time-Domain Method, 2d ed. (2000), with periodicboundary conditions. The result of either method is a modal dispersiondiagram for the eigenmodes of the structure, as shown in FIG. 2( b),from which the modal propagation constants may be extracted and hencethe coupling length necessary for full transmission of the optical powerfrom one waveguide to a nearby waveguide may be calculated.

Starting with the Supercell shown in FIG. 2( a), the PWM method was usedto numerically compute the Bloch propagation constants for a plane wavepropagating through the Supercell. The dispersion diagram obtained usingthe PWM method is shown in FIG. 2( a). On the other hand, if the FDTDmethod was used, a set of normalized propagation constants in the range(0<β2π/a<0.35) with an interval Δβ=0.01×2π/a would be used. In order tocategorize the odd and the even modes, excitations of a TM-even mode anda TM-odd mode were launched, from which it was found that eigenmodeswith lower frequencies belong to the even mode, while the higherfrequencies belong to the odd mode. The FDTD-generated dispersiondiagram may then be plotted over the dispersion diagram obtained fromthe PWM method. As shown in FIG. 2( a), both dispersion diagrams overlapfor a great extent.

From the modal dispersion curves (FIG. 2( b)), the length necessary fora signal launched in waveguide 12 to completely transfer to waveguide 14may be calculated using the following procedure. For a specificfrequency, the corresponding values of the normalized modal Bloch phaseconstants, for the even β_(e) and the odd β₀ eigenmodes, are found. Thecoupling length L_(c) required for full transmission can be thencalculated using the following Equation:

$\begin{matrix}{L_{c} = {\frac{\pi}{\left( {\beta_{e} - \beta_{o}} \right)}.}} & (1)\end{matrix}$

By way of example only, for the device shown in FIG. 1, a wavelength of1550 nanometers (nm) (a/λ=0.35) was used, where a=542.5 nm, r=108.5 nm.From FIG. 2( b), the propagation constant of the odd and even modes arefound: (β₀=2π×0.1977/a=2.357×10⁶ m⁻¹) and (β_(e)=2π×0.2154/a==2.568×10⁶m⁻¹), from which the full coupling length may L_(c) be calculated usingthe following Equation:

$\begin{matrix}\begin{matrix}{L_{c} = {{\pi/\left( {2.568 - 2.357} \right)} \times 10^{6}}} \\{= {14.88\mspace{14mu}{µm}}} \\{= {14.88\mspace{14mu}{{µm}/0.5425}\mspace{14mu}{µm}}} \\{= {28a}} \\{= {9.6{\lambda.}}}\end{matrix} & (2)\end{matrix}$

Thus, the complete transmission from one waveguide to the other requiresapproximately ten (10) wavelengths to occur, making such a theory viablefor high density photonic integrated circuit applications.

In the case of a perforated silicon slab, which may be used as aneffective index approximation to simplify a three-dimensional (3D)computational problem to a two-dimensional (2D) problem, then_(eff)=2.88 may be calculated for the slab by solving thetranscendental equation set forth in A. Yariv et al., Optical waves inCrystals (1984). Air holes of radius r/a=0.3 may be arranged in ahexagonal lattice. Using these values, the structure was found to have abandgap in the spectral range of 0.24786≦a/λ≦0.3131 for TE polarization(electric field in plane). A full 3D structure consisting of aperforated slab of air holes arranged in a hexagonal lattice, a slabthickness t/a=0.6 and air holes radii of r/a=0.3 may be used in thenumerical experiment. For such a structure, the bandgap was found to bein the spectral range of 0.2475≦a/λ≦0.3125 for the TE-like mode (evenmode). Hence, effective index approximation may be used to reducecomputational time and space.

FIG. 3 shows a CPhCW system in accordance with another aspect of thepresent invention and generally designated by reference numeral 30.CPhCW 30 includes two closely coupled PBG waveguides 32, 34 separated bytwo PBG layers of coupling length L_(c). CPhCW system 30 is formed usinga periodic array of air holes 36 arranged in a hexagonal lattice 38.Waveguide 32 includes two input/output ports, Port 1 (40) and Port 2(42), and waveguide 34 has two input/output ports, Port 3 (44) and Port4 (46).

To obtain the modal dispersion of the even mode and the odd mode, theeigenmodes within the Supercell shown in bottom right corner of FIG. 2(c) is numerically solved using the PWM method. Again, the only focus ison the modal dispersion curves within the bandgap of the structure(0.2475≦a/λ≦0.3125), as shown in FIG. 2( d). Once the modal dispersioncurves are obtained for both the odd and even modes, the frequencydependant coupling length L_(c) may be obtained following the sameprocedure presented above for the case of dielectric pillars.

By way of example only and not limitation of the present invention,assume a wavelength of 1550 nm (a/λ=0.27) is used, where a=418.5 nm,r=125.5 nm. FIG. 2( d) shows the propagation constant of the odd mode(β₀=2π×0.2034/a=3.054×10⁶ m⁻¹) and the propagation constant of the evenmode (β_(e)=2π×0.2359/a=3.541×10⁶ m⁻¹), from the and the full couplinglength L_(c) may be calculated using the following Equation:

$\begin{matrix}\begin{matrix}{L_{c} = {{\pi/\left( {3.541 - 3.054} \right)} \times 10^{6}}} \\{= {6.44\mspace{14mu}{µm}}} \\{= {6.44\mspace{14mu}{{µm}/0.4185}\mspace{14mu}{µm}}} \\{= {16a}} \\{= {4.0{\lambda.}}}\end{matrix} & (3)\end{matrix}$

Comparing the modal dispersion curves of the even and odd modes in FIG.2( d), shows that, unlike the silicon pillar case (CPhCW 10) wherehigher frequency modes belong to the odd mode, and lower frequency modesbelong to the even mode, for the perforated slab case (CPhCW 30) higherfrequency modes belong to the even mode, and lower frequency modesbelong to the odd mode.

Once the modal dispersion relations have been numerically extracted, thenext step is to utilize the frequency dependence of such relations todesign an optical switch in PhC waveguides for both the dielectric rodsin an air background case, as well as air holes in a silicon backgroundcase.

2. Switching Approach

The “loss tangent” of dielectric material in the coupling region can bemodified by external “commands” to spoil the coupling, therebyre-routing the light. This is what is known as a Δα switch (not theclassical Δβ switch) in which the change in optical absorptioncoefficient Δα is employed. The change in conductance Δσ is proportionalto Δα. The present inventors have found that the induced loss does notsignificantly attenuate the waves traveling in the straight-throughchannels. This behavior is analogous to that discussed in R. A. Soref etal., “Proposed N-Wavelength M-Fiber WDM Crossconnect Switch Using ActiveMicroring Resonators,” IEEE Photonics Technology Letters, vol. 10, pp.1121-1123 (August 1998), where electro-absorption was assumed to reducethe Q of micro-ring resonators coupled to strip channel waveguides. Toattain switching in 2D-PhC waveguides made from silicon and air (Si/air)or silicon and silicon dioxide (Si/SiO₂), the free-carrier absorptionloss of Si can be controlled by: (1) carrier injection fromforward-biased PN junctions on the posts; (2) depletion of doped postswith MOS gates; and (3) generation of electrons and holes by above-gaplight shining upon the designated pillars, which is a contact-freeprocess. If the PBG coupler is implemented in III-V semiconductorheterolayers, then the electro-absorption effect could be used. TheCPhCW systems of the present invention differ from the conventional PBGswitching device of Fan et al. (cited above), which relies upon apoint-defect resonator, or two point defects, situated between two PBGchannels. Fan et al. assumed that the Q of those cavities would bespoiled by loss induced electrically at the defects.

3. Numerical Analysis of the Switch

For the 1550 nanometer (nm) center wavelength, an exemplary 2D photoniccrystal may be provided having 217 nm diameter silicon dielectric rods(ε_(r)=11.6) arrayed in a square lattice (a=542.5 nm) on an airbackground. Line defects and bent lines define the channel waveguides.PBG waveguides of the present invention are analogous to the practical2D e-beam-etched silicon waveguide system developed by M. Loncar et al.,“Waveguiding in Planar Photonic Crystals,” Applied Physics Letters, vol.77, pp. 1937-1939 (Sep. 25, 2000).

For the perforated slab, an exemplary 2D photonic crystal hexagonallattice may be provided having air holes with 251 nm diameters and alattice constant a=418.5 nm. The slab had an effective index ofn_(eff)=2.88. In this analysis, the FDTD method with perfectly matchedabsorbing boundary conditions around the rectangle enclosing the 2×2switch was used to truncate the computational domain and minimizereflections from the outer boundary. The full wave solution for forwardand backward traveling waves was solved alternately for E and H fieldsat different spatial points (e.g., at a λ/20 sampling rate) as timeprogressed. Examination of several switching test structures at aconductivity a approaching zero, showed that a coupling length L_(c)=28afor the square lattice, and a coupling length L_(c)=16a for thehexagonal lattice of the parallel-channel interaction region ensuredthat approximately 100% of the optical power launched into Port 1 (20,40) was transferred to the other waveguide and output at Port 3 (24,44). The spectral transmission of this coupler was analyzed and found tohave a periodic response whose first peak has a Full Width Half Maximum(“FWHM”) pass-band of about 20 mm.

4. Results

For a given value of conductivity (σ) and assuming unity power input toPort 1, the power emerging from Ports 2, 3, and 4, respectively, can bedetermined. The switching response as a function of conductivity a isshown in FIG. 4 for the square lattice device (CPhCW 10). Thetransmissions (“T”) were found to be: T(Port 2)>81% for σ>30 Ω⁻¹cm⁻¹ andT(Port 3)>88% for σ<0.0003 Ω⁻¹cm⁻¹. At σ=10⁻⁴ Ω⁻¹cm⁻¹, the predictedcrosstalks (“CT”) were found to be: Forward CT=Port 2/Port 3=−29.4 dB,Backward CT=Port 4/Port 3=−27.3 dB, while for σ=100 Ω⁻¹cm⁻¹, ForwardCT=Port 3/Port 2=−23.1 dB, Backward CT=Port 4/Port 2=−28.6 dB.

The switching response for the hexagonal lattice device (CPhCW 30) isshown in FIG. 5. The transmissions were found to be: T(Port 2)>85% forσ>10⁵ Ω⁻¹cm⁻¹ and T(Port3)>90% for σ<10² Ω⁻¹cm⁻¹. At σ=10 Ω⁻¹cm⁻¹, thepredicted crosstalks were found to be: Forward CT=Port 2/Port 3=−22.2dB, Backward CT=Port 4/Port 3=−23 dB, while for σ=3×10⁵ Ω⁻¹cm⁻¹, ForwardCT=Port 3/Port 2=−32.2 dB, Backward CT=Port 4/Port 2=−36.9 dB.

The switching responses shown in FIGS. 4 and 5 show that there is aminimum value for the output optical power at various ports for aspecific value of conductivity (σ=0.1 Ω⁻¹cm⁻¹) for the square latticedevice (CPhCW 10) and (σ=10⁴ Ω⁻¹cm⁻¹) for the hexagonal lattice device(CPhCW 30). At this transient value, the optical power launched at theinput port will be absorbed in the coupling region between the twowaveguides and the devices suffer a high attenuation coefficient α inthe coupling region. An increase or decrease in the conductivity willredirect the optical power to either bar- or cross-states respectively.

CPhCW 10 and CPhCW 30 be interconnected and cascaded in the forwarddirection into an N×N optical cross-connect network. In this case,further optimization to crosstalk may be achieved by minimizing thereflections at the waveguide bends. Techniques for enhancingtransmission through waveguide bends and hence reducing reflectionsinclude, broadband techniques (as set forth in A. Chutinan et al.,“Wider bandwidth with high transmission through waveguide bends intwo-dimensional photonic crystal slabs,” Appl Phys. Lett., vol. 80, pp.1698-1700 (2002) and A. Chutinan et al., “Waveguides and waveguide bendsin two-dimensional photonic crystal slabs,” Phys. Rev. B, vol. 62, pp.4488-4492 (2000)), and narrowband techniques (as set forth in C. J. M.Smith et al., “Low-Loss Channel Waveguides with Two-Dimensional PhotonicCrystal Boundaries,” Appl. Phys. Lett., vol. 77, pp. 2813-2815, (2000)and S. Fan et al., “Waveguide branches in photonic crystals,” J. Opt.Soc. Am. B, vol. 8, pp. 162-165, (2001)).

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the electro-opticalswitching in a photonic bandgap waveguided coupler of the presentinvention and in construction of this device without departing from thescope or spirit of the invention. As an example, the material selectionsand dimensions discussed above are purely exemplary and not limiting ofthe present invention.

Other embodiments of the invention will be apparent to those skilled inthe art from consideration of the specification and practice of theinvention disclosed herein. It is intended that the specification andexamples be considered as exemplary only, with a true scope and spiritof the invention being indicated by the following claims.

1. An electro-optical switch, comprising: a non-piezoelectric photoniccrystal having first and second waveguides separated by a region of thephotonic crystal, each of the first and second waveguides having 1) arespective input portion and a respective output portion and 2) acoupling length where the first waveguide is proximate to the secondwaveguide; and electrical means or optical means for inducing a changein conductance in the region of the photonic crystal along the couplinglength, wherein the respective input portions are unconnected to eachother, and the switch is configured such that the change in theconductance produces electro-optical switching between the first andsecond waveguides.
 2. An electro-optical switch as recited in claim 1,wherein said photonic crystal comprises a periodic array of siliconpillars arranged in a square lattice.
 3. An electro-optical switch asrecited in claim 1, wherein said photonic crystal comprises a periodicarray of air holes arranged in a hexagonal lattice.
 4. Anelectro-optical switch as recited in claim 1, wherein the propagationconstants of the first and second waveguides are different.
 5. Anelectro-optical switch as recited in claim 4, wherein the first andsecond waveguides electro-optically couple to each other over a range ofoptical wavelengths.
 6. An electro-optical switch as recited in claim 1,wherein the first and second waveguides are different.
 7. Anelectro-optical switch as recited in claim 6, wherein the first andsecond waveguides electro-optically couple to each other over a range ofoptical wavelengths.
 8. The electro-optical switch of claim 1, whereinthe change in conductance along the coupling length is induced byelectrical carrier injection provided by a forward-biased PN junction.9. The electro-optical switch of claim 1, wherein the electrical oroptical means is configured to modulate a coupling coefficient betweenthe first and second waveguides.
 10. A photonic bandgap integratedcircuit, comprising: a non piezoelectric photonic crystal; and anelectro-optical switch formed by providing first and second waveguidesin said photonic crystal separated by a region of the photonic crystaland electrical means or optical means for inducing a change inconductance in the region of the photonic crystal along a couplinglength, wherein the integrated circuit is configured such that thechange in the conductance produces electro-optical switching between thefirst and second waveguides, wherein the first and second waveguideseach have 1) a respective input portion and a respective output portion,the respective input portions being unconnected to each other and 2) thecoupling length where the first waveguide is proximate to the secondwaveguide.
 11. A photonic bandgap integrated circuit as recited in claim10, wherein said photonic crystal comprises a periodic array of siliconpillars arranged in a square lattice.
 12. A photonic bandgap integratedcircuit as recited in claim 10, wherein said photonic crystal comprisesa periodic array of air holes arranged in a hexagonal lattice.
 13. Aphotonic bandgap integrated circuit as recited in claim 10, wherein thepropagation constants of the first and second waveguides are different.14. A photonic bandgap integrated circuit as recited in claim 13,wherein the first and second waveguides electro-optically couple to eachother over a range of optical wavelengths.
 15. A photonic bandgapintegrated circuit as recited in claim 10, wherein the first and secondwaveguides are different.
 16. A photonic bandgap integrated circuit asrecited in claim 15, wherein the first and second waveguideselectro-optically couple to each other over a range optical wavelengths.17. The photonic bandgap integrated circuit of claim 10, wherein thechange in conductance along the coupling length is induced by electricalcarrier injection provided by a forward-biased PN junction.
 18. Thephotonic bandgap integrated circuit of claim 10, wherein the electricalor optical means is configured to modulate a coupling coefficientbetween the first and second waveguides.
 19. A coupled photonic crystalwaveguided system, comprising: first and second photonic bandgapwaveguides separated by a region of a non piezoelectric photoniccrystal; and electrical means or optical means for inducing a change inconductance in the region of the photonic crystal along a couplinglength, wherein the system is configured such that the change in theconductance produces electro-optical switching between said first andsecond photonic bandgap waveguides, wherein the first and secondwaveguides each have a 1) respective input portion and a respectiveoutput portion the respective input portions being unconnected to eachother and 2) the coupling length where the first waveguide is proximateto the second waveguide.
 20. A coupled photonic crystal waveguidedsystem as recited in claim 19, wherein the photonic crystal comprises aperiodic array of silicon pillars arranged in a square lattice.
 21. Acoupled photonic crystal waveguided system as recited in claim 19,wherein the photonic crystal comprises a periodic array of air holesarranged in a hexagonal lattice.
 22. A coupled photonic crystalwaveguided system as recited in claim 19, wherein the propagationconstants of said first and second photonic bandgap waveguides aredifferent.
 23. A coupled photonic crystal waveguided system as recitedin claim 22, wherein said first and second photonic bandgap waveguideselectro-optically couple to each other over a range of opticalwavelengths.
 24. A coupled photonic crystal waveguided system as recitedin claim 19, wherein said first and second photonic bandgap waveguidesare different.
 25. A coupled photonic crystal waveguided system asrecited in claim 24, wherein said first and second photonic bandgapwaveguides electro-optically couple to each other over a range ofoptical wavelengths.
 26. The coupled photonic crystal waveguided systemof claim 19, wherein the change in conductance along the coupling lengthis induced by electrical carrier injection provided by a forward-biasedPN junction.
 27. The coupled photonic crystal waveguided system of claim19 wherein the electrical or optical means is configured to modulate acoupling coefficient along the coupling length.
 28. A method forproviding an electro-optical switch, comprising: providing anon-piezoelectric photonic crystal; providing first and secondwaveguides in the photonic crystal separated by a region of the photoniccrystal, each of the first and second waveguides having a couplinglength where the first waveguide is proximate to the second waveguide;and inducing a change in conductance in the region of the photoniccrystal along the coupling length to produce electro-optical switchingbetween the first and second waveguides, wherein the first and secondwaveguides each have a respective input portion and a respective outputportion, the respective input portions being unconnected to each other.29. A method for providing an electro-optical switch as recited in claim28, wherein the photonic crystal comprises a periodic array of siliconpillars arranged in a square lattice.
 30. A method for providing anelectro-optical switch as recited in claim 28, wherein the photoniccrystal comprises a periodic array of air holes arranged in a hexagonallattice.
 31. A method for providing an electro-optical switch as recitedin claim 28, wherein the propagation constants of the first and secondwaveguides are different.
 32. A method for providing an electro-opticalswitch as recited in claim 31, wherein the first and second waveguideselectro-optically couple to each other over a range of opticalwavelengths.
 33. A method for providing an electro-optical switch asrecited in claim 28, wherein the first and second waveguides aredifferent.
 34. A method for providing an electro-optical switch asrecited in claim 33, wherein the first and second waveguideselectro-optically couple to each other over a range of opticalwavelengths.
 35. The method for providing an electro-optical switch ofclaim 28, wherein said changing the conductance along the couplinglength comprises injecting electrical carriers provided by aforward-biased PN junction.
 36. The method for providing anelectro-optical switch of claim 28, wherein said changing theconductance along the coupling length comprises modulating a couplingcoefficient between the first and second waveguides.
 37. The method forproviding an electro-optical switch of claim 28, wherein said changingthe conductance along the coupling length comprises changing an opticalabsorption along the coupling length.
 38. An electro-optical switch,comprising: a non-piezoelectric photonic crystal having first and secondwaveguides separated by a region of the photonic crystal, wherein eachof the first waveguide and the second waveguide have a coupling lengthwhere the first waveguide is proximate to the second waveguide; andmeans for inducing a change in conductance in the region of the photoniccrystal along the coupling length, wherein the switch is configured suchthat the change in the conductance produces electro-optical switchingbetween the first and second waveguide, wherein the change inconductance along the coupling length is optically induced byelectron-hole pair generation.
 39. A photonic bandgap integratedcircuit, comprising: a non-piezoelectric photonic crystal; and anelectro-optical switch formed by providing first and second waveguidesin said photonic crystal separated by a region of the photonic crystaland means for inducing a change in conductance in the region of thephotonic crystal along a coupling length, wherein the integrated circuitis configured such that the change in the conductance produceselectro-optical switching between the first and second waveguides,wherein the change in conductance along the coupling length is opticallyinduced by electron-hole pair generation and the first waveguide isproximate to the second waveguide along the coupling length.
 40. Acoupled photonic crystal waveguided system, comprising: first and secondphotonic bandgap waveguides separated by a region of a non-piezoelectricphotonic crystal; and means for inducing a change in conductance in theregion of the photonic crystal along a coupling length, wherein thesystem is configured such that the change in the conductance produceselectro-optical switching between said first and second photonic bandgapwaveguides, wherein the change in conductance along the coupling lengthis induced optically by electron-hole pair generation, and the firstwaveguide is proximate to the second waveguide along the couplinglength.
 41. A method for providing an electro-optical switch,comprising: providing a non-piezoelectric photonic crystal; providingfirst and second waveguides in the photonic crystal separated by aregion of the photonic crystal, each of the first and second waveguideshaving a coupling length where the first waveguide is proximate to thesecond waveguide; and inducing a change in conductance in the region ofthe photonic crystal along the coupling length to produceelectro-optical switching between the first and second waveguides,wherein said changing the conductance along the coupling lengthcomprises optically inducing electron-hole pair generation.